The present invention generally relates to measurement probes and more particularly to a hand-held probing adapter for a measurement probing system.
As the bandwidth of measurement instruments, such as oscilloscopes and the like, increases, there is a corresponding need for measurement probes having equal or greater bandwidths. A major difficulty in designing very wide bandwidth measurement probes having bandwidths of 5 Ghz and greater is the effects of capacitance and inductance of the probing tip or tips. One solution to this problem is to separate the probing tips from the active circuitry in the probing head of the measurement probe. U.S. Pat. No. 6,704,670 describes a wideband active probing system where the probing tip or tips of the probe are separable from a probe amplifier unit. One or more probe cables are connected to a probe tip unit which are connected to the probe amplifier unit for conveying signals received by a probe unit. Various types of probe tip units may be connected to the probe amplifier unit. The probe tip unit may contain circuitry ranging from conductor traces to various resistive, capacitive, and/or other electronic elements. An advantage of such a probe design is that it allows the placement of the substantially smaller probe tip unit onto difficult to reach contacts on a device under test instead of a larger measurement probe containing probe amplifier circuitry.
One type of probe tip unit for the wideband active probing system is a differential probe unit. The differential probe unit includes a probe unit housing and probe assemblies. Each probe assembly includes a probe barrel, a probe barrel nose cone and a probing tip. The center conductor of the probe cable is electrically coupled to the probing tip and an outer shielding conductor of the probe cable is electrically coupled to the probe barrel. The probe barrels are partially disposed within the probe housing with the probe barrel nose cones attached to the respective probe barrels extending outward from the probe housing. The probing tips extend partially out of the respective probe barrel nose cones. The longitudinal axis of each probe barrel nose cone is offset at an angle from the longitudinal axis of its respective probe barrel. The probe barrels are rotatable within the probe unit housing. This allows the probing tips to be rotated to various separation distances to match the separation distances of probe points on a device under test. The differential probe unit further includes elastic compressible elements that allow the probe assemblies to move along the longitudinal axis of the probe barrels for mating with probe points of differing heights on the device under test.
While the above describe design is excellent for wideband probing, the overall performance may be affected by the use of attachable probe tip units. Each probe tip unit has particular electrical characteristics that need to be matched to the probe head amplifier or compensated for by calibration. If the electrical characteristics of the probe tip units are not compensated for by calibration, then the overall performance of the probing system may be downgraded. This then would require re-calibration of the probing system each time a different probe tip unit is attached to the probe head amplifier. A unitary measurement probing system where a single probe tip unit is permanently attached to the probe head amplifier via one or more coaxial cables would allow for the electrical characterization and generation of single set of calibration constants for the measurement probing system. Thus the measurement probing system would only need to calibrated with the measurement instrument at the time the measurement probing system is attached to the measurement instrument. However, such a measurement probing system would be limited to the design of the probe tip unit. For example, if the probe tip unit is designed for hand-held probing, such as the above described differential probe tip unit, then it would be difficult to physically attach the differential probe tip unit to the device under test via soldering or the like.
What is needed is a hand-held probing adapter for a measurement probing system having a permanently attached probe tip unit or member that allows the measurement probing system to be used for hand-held probing applications as well as applications where the probe tip member is fixedly attached to the device under test. The hand-held probing adapter needs to easily attachable and detachable from the measurement probing system. The hand-held probing adapter further needs to allow lateral rotational and axis movement of the probe tip member for making electrical contact with probing points of differing heights on the device under test.